I have ordered one powerwall and I am being told that I cannot hook up my main house subpanel to it. Apparently I need to only hook up critical loads to the PW. I don't get it. Isn't the PW protected by a 30A breaker anyway? It's pretty obvious that stove and dryer would not work with a PW, but I want to keep all my lights, fridge and some outlets on during an outage. Also, they want to derate my main panel by 25A. Does anybody have a clue as to the why?
The NEC requires that an automatic standby power system be sized to handle the connected loads. Tesla doesn't actually comply with this, but what they do is insist that with (n) Powerwalls installed, only branch circuits on breakers of size (30n) or less are backed up. So with only 1 Powerwall, they want only 30 amp or smaller breakers behind the Backup Gateway. As to downsizing the main breaker in your main panel (what I assume you mean by derate), do you have solar? When a panel can be supplied by multiple sources (e.g. the utility and the Powerwall; or the utility and solar; or all three), the NEC has rules to ensure that the panel's bus does not get overloaded. Usually there is some headroom available in an existing panel when adding a first alternate source (the so-called 120% rule). But if you already have solar, then the solar generation may have used the available headroom, meaning that adding the Powerwall requires reducing the current the utility can provide to the panel bus. Cheers, Wayne
I know the PW is a splitphase, is it a 30A total (15A per line) or 30A per line? If it's a 2x15A then running a fridge alone might be difficult. Some of those fridges require a 15A dedicated breaker; heck the older larger 2 compressor built in fridges would pull about 25A on their own. FWIW; I skimmped out on my first system. I have 75A peak, 60A continuous ability with about 6kW/4 hours of backup on a critical loads panel. The reason it's on a critical load panel is because if it backed up the entire panel; it would trip anytime I plugged my cars in. The system would be designed to trip and protect itself using a 70A breaker; which means plugging in a car that charges at 72A would automatically trip that breaker and send it into protection mode and everything would shut off. By putting it on a seperate panel; the 72A of the car "bypasses" the critical loads panel and is fed directly from the main house panel. The critical loads panel then supplies everything else on that panel up until the 70A limit. In hindsight; I should have (and will now) spend the extra money and done a full 200A backup of the main panel. But hope this helps.
Thanks Wayne foe the thorough explanation. That 120% rule is so silly. It's not like electricity can travel both ways at the same time. Got the 40A rule. So, with 2 powerwalls, I would back up the whole house then. Good to know.
I have my entire house backed up on a single powerwall 2 except my AC (30amp) and Tesla Wall Connector (60amp). So basically the 125 amp subpanel that controls the rest of my house is all backed up by the powerwall. That includes my furnace, electric dryer, two refrigerators for around 20 or so breakers in that subpanel. It's funny because they told me the opposite. When the guy came out for the site survey, he told me to pick 6 breakers that I wanted backed up. So I went through and found them and labeled them. Then on the day of install they told me they're just backing up the entire 125 amp subpanel so I didn't need to pick 6 of those breakers.
Sure it can... the 120% rule exists to protect the bus. If you have a 200A main breaker and 100A of solar you could exceed the bus rating of ~240A since current can flow in from the main breaker AND the solar breaker.
Depends on how they're wired. If the subpanel is fed from the main panel then it would flow in from the sub panel and the main breaker. The 120% rule would apply to the panel which could be fed by both.
Well quote for a second powerwall is over $12k. Strongly considering giving up on installer and just wait for Tesla to call my number.